Change value in a matrix with a conditional statement

I have a matrix [3000,1000] which only consist of 1,-1,0,-2. If there is -1 in a row followed by any consecutive zeros then followed by 1, this 1 value should change to 2. But if this -1 is followed by any consecutive zeros then followed by -2 and then followed by 1, this 1 value should remain the same.

For example

 A = [0 -1 0  0 1 0 -1 0 0  0 0 -2 0 0 0 1;
     -1  0 0 -2 0 1  0 0 0 -1 0  0 0 0 1 0]

should change to

 A = [0 -1 0  0 2 0 -1 0 0  0 0 -2 0 0 0 1;
     -1  0 0 -2 0 1  0 0 0 -1 0  0 0 0 2 0]

Any suggestion would be very helpful.

Thank you

Answer 1

[Sri Harish G]

If you are unwilling to iterate through the matrix and change the 1s at the appropriate location to a 2, you could convert the rows of the matrix to a string and search for the regular expression '-1[0]*1' and replace the element in the ending index of all matches with a 2.

https://www.mathworks.com/help/matlab/ref/regexp.html

Example:

>> A=[0 -1 0  0 1 0 -1 0 0  0 0 -2 0 0 0 1;
         -1  0 0 -2 0 1  0 0 0 -1 0  0 0 0 1 0];

>>B=cellstr(num2str(A))

   B =

   2×1 cell array

       {' 0 -1  0  0  1  0 -1  0  0  0  0 -2  0  0  0  1'}
       {'-1  0  0 -2  0  1  0  0  0 -1  0  0  0  0  1  0'}

>>C=regexp(B,'-1[ 0 ]*1','end')

    C =

    2×1 cell array

       {[14]}
       {[44]}

 >>B=arrayfun(@(x,y) replace(x,y),B,C)

Where function replace is defined as:

    function out = replace(x,y)
          x{1}(y{1})='2';
          out=x;
      end

This will give

    B =

    2×1 cell array

      {' 0 -1  0  0  2  0 -1  0  0  0  0 -2  0  0  0  1'}
      {'-1  0  0 -2  0  1  0  0  0 -1  0  0  0  0  2  0'}

>>A=str2num(cell2mat(B))

   A = [0 -1 0  0 2 0 -1 0 0  0 0 -2 0 0 0 1;
       -1  0 0 -2 0 1  0 0 0 -1 0  0 0 0 2 0]